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Abstract We have measured, for the first time, the inclusive missing-mass spectrum of the $^{12}$C$(K^-, p)$ reaction at an incident kaon momentum of 1.8 GeV/$c$ at the J-PARC K1.8 beamline. We observed a prominent quasi-elastic peak ($K^-p \\rightarrow K^-p$) in this spectrum. In the quasi-elastic peak region, the effect of secondary interaction is apparently observed as a peak shift, and the peak exhibits a tail in the bound region. We compared the spectrum with a theoretical calculation based on the Green’s function method by assuming different values of the parameters for the $\\bar{K}$–nucleus optical potential. We found that the spectrum shape in the binding-energy region $-300 \\, \\text{MeV} < B_{K} < 40$ MeV is best reproduced with the potential depths $V_0 = -80$ MeV (real part) and $W_0 = -40$ MeV (imaginary part). On the other hand, we observed a significant event excess in the deeply bound region around $B_{K} \\sim 100$ MeV, where the major decay channel of $K^- NN \\to \\pi\\Sigma N$ is energetically closed, and the non-mesonic decay modes ($K^- NN \\to \\Lambda N$ and $\\Sigma N$) should mainly contribute. The enhancement is fitted well by a Breit–Wigner function with a kaon-binding energy of 90 MeV and width 100 MeV. A possible interpretation is a deeply bound state of a $Y^{*}$-nucleus system.

Abstract In the E373 experiment at KEK-PS, we have located nearly 2 $\\times$ 10$^4$ stopping events of ${\\Xi^-}$ hyperon candidates in nuclear emulsion. Among these, the identification of the ${\\Xi^-}$ hyperon was performed with the constant sagitta (CS) method, by measuring multiple Coulomb scattering for 695 clear stopping events, $\\sigma$-stop, with emission of nuclear fragments due to negatively charged hadrons. With use of a Geant4 simulation, the parameters for the CS method were optimized and we obtained the number of real ${\\Xi^-}$ stopping events to be $432.3 \\pm 7.6 ^{+~0.0}_{-14.0}$ with 3.2% systematic error by contamination by the $\\Sigma^-$ hyperon. We have classified the events for ${\\Xi^-}$ hyperon capture by light (C, N, O) and heavy (Ag, Br) elements in the emulsion. The trapping probabilities of two ${\\Lambda}$ hyperons for light and heavy nuclei were found to be $5.0 \\pm 1.7\\%$ and $4.2 \\pm 1.4\\%$, respectively, for $\\sigma$-stop via ${\\Xi^-}$ hyperon capture at rest in the emulsion. For at least one ${\\Lambda}$ trapping, the probabilities were $69.4 \\pm 8.1\\%$ for light nuclei and $51.1 \\pm 5.7\\%$ for heavy nuclei. These results allow us to present the trapping probabilities of ${\\Lambda}$ hyperons via ${\\Xi^-}$ hyperon capture at rest in emulsion for the first time, because the previous E176 experiment showed the lower limits due to fewer statistics.

Abstract A development has been achieved in the identification method of the charges 1 to 5 of nuclides from the decay of double hypernuclei to be uniquely recognized by their nuclear species. The method is basically the measurement of track volume by the widths, depths, and angles of tracks of exposed nuclei of $^1$H, $^4$He, $^7$Li, $^9$Be, and $^{11} $B in nuclear emulsion at RIken Projectile-fragment Separator of RIKEN Radioactive Isotope Beam Factory. After their calibration by $\\alpha$ particles, we obtained a quadric function to present a unified recognition of tracks with volume ratios of five nuclei to the $\\alpha$ particles. The function in the emulsion has been applied to a candidate event of a $\\Xi$ hypernucleus for identification of the production and decay processes. We succeeded in recognizing a daughter nuclear fragment of a single-$\\Lambda$ hypernucleus as $^6$He with a likelihood ratio of 0.9; the process was then uniquely identified as $\\Xi^-$ + $^{14}$N $\\rightarrow$${_\\Lambda}^9$Be + ${_\\Lambda}^5$He + $n$.

We performed a measurement of the inclusive missing-mass spectrum of the $^{12}$C$(K^-, K^+)$ reaction at an incident beam momentum of 1.8 GeV/c. This measurement was carried out by using the Superconducting Kaon Spectrometer (SKS) and the K1.8 beamline spectrometer at the Hadron Experimental Facility in J-PARC. From the missing-mass of the $^{12}$C$(K^-, K^+)$ reaction, the binding energy of a $\\Xi ^-$ hyperon in a core $^{11}$B nucleus, $B_{\\Xi ^-}$, can be calculated. Our experimental setup yielded a good energy resolution of 8.2 MeV (full width at half maximum), which allowed us to observe significant enhancements in the proximity of the $^{12}_{\\Xi }$Be production threshold region. In order to extract information from the missing-mass spectrum, we employed several fitting parameters assumptions. A good agreement with the spectrum shape was obtained by adding two Gaussian functions, with the constant experimental resolution for the $\\Xi$-hypernuclear states, to the background distribution. The peak positions were obtained to be $B_{\\Xi ^-} = 8.9 \\pm 1.4$ (stat.) $^{+3.8}_{-3.1}$ (syst.) MeV and $B_{\\Xi ^-} = -2.4 \\pm 1.3$ (stat.) $^{+2.8}_{-1.2}$ (syst.) MeV. Another model assumption, one Breit–Wigner function with $B_{\\Xi ^-} = -2.7 \\pm 2.2$ (stat.) $^{+0.5}_{-0.7}$ (syst.) MeV and $\\Gamma = 4.1 \\pm 2.1$ (stat.) $^{+1.2}_{-0.7}$ (syst.) MeV, also yielded a similar $\\chi ^2$ value.

With use of nuclear emulsion, double-hypernuclei have been studied for aiming to understand Λ-Λ interaction via at-rest-capture of Ξ− hyperon originated by quasi-free (K−, K+) reactions, where the beam K− momentum was 1.66 GeV/c. Under the process for studying them, elementary feature for not only quasi-free reaction but also production of nuclei with single and double unit(s) of strangeness have been roughly understood, even the statistics were not large. So far we have succeeded to analyze 5 events of double-hypernuclei which introduced binding energies of two A hyperons on several nuclei. However its knowledge is very limited. We have started a new experiment, J-PARC E07, to give us rich information in S −2 world. An event which may give us a new information about Ξ-nucleus interaction shall be introduced.

With use of nuclear emulsion, double-hypernuclei have been studied for aiming to understand [Lambda]-[Lambda] interaction via at-rest-capture of [Xi] super(-) hyperon originated by quasi-free (K super(-), K super(+)) reactions, where the beam K super(-) momentum was 1.66 GeV/c. Under the process for studying them, elementary feature for not only quasi-free reaction but also production of nuclei with single and double unit(s) of strangeness have been roughly understood, even the statistics were not large. So far we have succeeded to analyze 5 events of double-hypernuclei which introduced binding energies of two [Lambda] hyperons on several nuclei. However its knowledge is very limited. We have started a new experiment, J-PARC E07, to give us rich information in S = -2 world. An event which may give us a new information about [Xi]-nucleus interaction shall be introduced.